two angles to look at:
1. If you don't have speed -- slow 400m--or haven't done the workouts to develop speed, then what you did looks about right.
As you head to college--I'm guessing you intend to go--and you are a walk-on, you could develop and run some pretty good times as you get older and stronger (difference between 18 and 22 years of age).
2. If you have speed--and you haven't discussed your 400m or 800m times---then I think you ran too much in HS and should not increase the mileage in college.
If the coach wants runners up in 70-80 mile range, or more, I would be hesitant to follow that doctrine. I was fast, and I trained with some runners who were well known in track circles, and that kind of mileage is often frowned upon, because the legs are "too dead" to run sharp times in intervals.
One thing is almost for certain: the college coach will have the runners do more intervals that you experienced in HS, and at faster paces.